Cobalt bromide relative humidity indicators



Patented Jan. 25, 1949 coBAL'r'BTtoMmE RELATIVE HUMIDITY INDICATORS Paul Bell Davis, Baltimore, Md., assignor to The Corporation, Baltimore,

Davison Chemical Md.

No Drawing. Application February 7, 1945, Serial N0. 576,720

2 Claims. (Cl. 252-408) This invention relates to indicators and more particularly has reference to compositions for indicating the presence of moisture in a gaseous atmosphere.

An object of this invention is to provide a composition forindicating the presence and quantity of moisture in a gaseous atmosphere within predetermined limits, j

Another object of this invention is to provide a composition capable ofexhibiting a definite color break when exposed to a gaseous atmosphere having a relative humidity ranging from about 5 to percent.

A further object of this invention is to provide a moisture indicator formed of cobalt bromide associated with an adsorbent carrier such as silica ge Still another object of this invention is to provide a moisture indicator formed of an adsorbent material such as silica gel having CoBrz incorporated in the pores thereof in which the adsorb ent characteristics of the adsorbent material, its moisture content, the color changing characteristics of the CoBrz and its concentration are correlated to produce a definite break in the color of the indicator when exposed to a gaseous atmosphere having a predetermined relative humidity. It is also an object of this invention to provide a method of making a color changing moisture indicator.

Additional objects will appear hereinafter in the following description.

In accordance with the present invention it has been found that by treating an adsorbent carrier such as silica gel with an aqueous solution of CoBrz and drying the so-treated carrier,

an indicator gel is obtained which is a definite color and which upon exposure to a gaseous atmosphere such as air having a predetermined relative humidity will change its color. It has also been found in accordance with the present invention that by correlating the adsorptive characteristics of the carrier its final moisture content as fixed by the temperatures at which the impregnated carrier is dried or dried and activated and the concentration of cobalt bromide in the carrier itself, the color of the resulting indicator before exposure to a humid atmosphere and also the color of the indicator after exposure to an atmosphere having a predetermined relative humidity can be adjusted or controlled.

The present invention is directed principally to moisture indicators formed of a carrier such as silica gel impregnated with cobalt bromide and having a definite color change or break when exposed to a gaseous atmospheresuch as air having a relative humidity in the range of 5 to 10%.

In preparing an indicator according to the present invention, a standard silica gel made by washing an acid reacting hydrogel with an acidic wash water at a temperature of about 150 F.. drying and then activating it at a temperature of about 850 F. and of a size about fi-lfimesh was employed. The silica 'gelin the activated form was first treated by exposing it to a humid atmosphere having a high relative humidity to saturate the gel with moisture to such an extent-that upon contacting it with a liquid it would not disintegrate as is the case of freshly activating gel upon contacting it with a liquid.

After saturation with moisture to a total volatile content of about 30%, the gel was impregnated with an aqueous solution of cobalt bromide. It has been found that by first saturating the gel with moisture to the extent indicated, wetting of the gel with the cobalt bromide solution can be effected by using about 50 ml. of solution per kilogram of the gel. Of course, if desired, more of the solution can be employed. The cobalt bromide solution used was of such concentration and the quantity of the solution per kilogram was such that the gel has a COBIz content of about on a dry basis. I

By drying a silica gel having a CoBrz content or about 4% at a temperature of about 275 F. and activating it at a temperature of about 400 F., an indicator gel was obtained having a Munseli color value of about 5.0 B 3/6. This indicator gel was found to be particularly suitable for the indication of the presence of moisture in a gaseous atmosphere, such as air, when the content of moisture in the atmosphere was in the range of 5 to 10% relative humidity. For instance, when this indicator gel Was exposed to an atmosphere having a relative humidity of about 5%, the color changed to about 7.5 B 7/2 M. C. V. Upon exposing this same indicator gel to an atmosphere having a relative humidity of about 10%, the color changed to about 7.5 R 8 /4 M. C. V.

In the drying and activating of the above-mentioned gel the same was held at the temperature indicated for about 3 hours.

While silica gel has been described as the carrier of the cobalt bromide, a porous glass may be used as described in my copending application Serial No. 576,726 (now abandoned), filed of even date herewith. Such porous glass is made from a glass containing from to 82% SiOz, 20 to 35%. B203 and 5 to 10% alkali oxide heat treated at a 4, perature of about 400 1",, said indicators changing color when exposed to an atmosphere having a relative humidity of 5-10 maintained at a temperature at or near the boil-.

ing point thereof, the acid reacts with the alka-- line phase of the glass forming a number of 'microscopic pores throughout the body thereof.

This porous glass may silica gel hereinbefore mentioned.

be used in place :of. the

The values given for the various colors in the 1 foregoing description'refer to the system of color notation devised by A. H. Munsell and published by Munsell Color Company, Inc, Baltimoi'e Maryland, as the Munsell Book of Color, abridged I edition, revised 1942.

From the foregoing description, it will be appreciated that the present invention provides an indicator gel particularly suitable for the inclica tlon of the relative humidity of theatmosphere. It Will also be appreciated that the present invention provides a method of indication having a color break when exposed to an atmosphere having a predetermined relative humidity.

I claim: V v 1. A method of preparing a quantitative relative humidity indicator comprising impregnating activated silica gel with about on a dry basis, of cobalt bromide, drying the impregnated silica gel'at a temperature of about 1275'" R, and activating the impregnatedsilica gel at a tem- 5 fiie of thispatentz V V UNITED STATESPATENTS' Number Name Date 1,9f7,381 Connolly 'et a1 Feb. 13, 1934 20 1,976,875 Connolly 'et a1. Oct. 16, 1934 2,210,862 Trcnstad Aug. 6, 1946 2,214,354 Snelling Sept. 10, 19 29 7 FOREIGN PATENTS 25 Number Country 7 Date.

a 280,934 Great Britain Feb. 18,1929 345,672 Great Britain Mar; 23, ,1931 393,094 Great Britain June 1, 1933 437,139 Great Britain Oct. 24, 1935 2. A quantitative relative humidity indicator consisting essentially of silica gel impregnated with about %%l; on a dry 'basis, of cobalt bromide, saidindicator changing color hen exposed ,to an atmosphere having a relative humidity ranging from 540% and being prepared by the method ofc'la-im 1-;

PAUL BELL DAVIS. 7 REFERENCES mm The following references are of record in the OT ER- REFERENCES The Chemical Trade Journal and Chemical Engineer, July 14, 1939, page 31. 

